Conventional "barrel-type" reciprocating bottom hole pumps have been used for many years as evidenced by the many thousands of pump-jacks across the country, each pump-jack reciprocating a sucker-rod string disposed vertically into a well so as to actuate the pump therein. Typically, the pump body is suspended near the bottom of a tubing string such that the pump is in the liquid to be pumped from the well. A conventional pump body is usually made from a joint of tubing and has an inlet to receive liquid from the producing formation into the pump chamber or "barrel." A piston is reciprocated within the pump chamber, allowing liquid to pass through a first check valve into the pump chamber during the return stroke and forcing that liquid up through a second check valve into the production tubing on the pump stroke. The piston is affixed to a piston rod of greater length than the pump stroke so as to allow the rod to pass through and be sealed by a seal member which prevents back flow from the production tubing into the pump chamber.
Although methods have been devised to vary the speed and lengths of pump strokes in an attempt to adjust to changing well conditions, such pumps do not pump at precisely the rate that the well may be producing at any given time. Such a mismatch often leads to: a lower production rate if the pumping is at too low a rate; or to pump damage and a waste of energy when the pump operates faster than the formation is then producing. Such pumps are also suseptable to vapor-lock wherein gas or vapor accumulates in the pump chamber and expands during the return stroke and thereby exerts a pressure within the pump chamber which in turn prevents liquid from filling the pump chamber whereupon the next pump stroke can pump only a fraction of its rated volume.
Although such pumps have operated reasonably well at low pressures and at shallow depths, they are not suited to operate while submerged in hot liquids as occurs in the steam flooding of formations producing heavy oils. Not only would seal materials fail but sucker-rod expansion due to the heat would inhibit proper performance as would reciprocation of sucker rods through the thickening heavy oil as it cools as it flows toward the surface.
The use of sucker rods in crooked holes causes extreme wear on both the rods and the casing which in turn invites casing failure, down time and loss of production.
Both rotary and reciprocating downhole pumps have been driven by pumping a portion of the fluid produced back down the hole through a separate conduit to actuate a bottom hole pump and then to exhaust into the production tubing and return to the surface along with new liquid from the formation. Such an arrangement requires that the power fluid pumped down be at a much higher pressure than the formation pressure. Also it is required that the net volume of oil produced is substantially less than the total volume pumped up the tubing because some must be returned to power the bottom hole pump. Such pumps are also subject to vapor-lock as well as the obvious loss of energy required to continually circulate the high pressure, power fluid. Since fluid produced from the formation will have fine sand particles entrained therein, so will the fluid separated at the surface for use as power fluid, making it necessary to filter and degas the fluid before admitting it to a high pressure surface pump. Even though filtered, fine abrasive particles remain in the fluid and act to damage the surface pump and the downhole pump as well.
Various gas lift methods have been employed on wells of limited depth. However, such a practice can be economically justified only if a sufficient quantity of gas at an excessive pressure is available. By nature, gas lift is inefficient and the cost to repressure gas for lifting a high liquid-gas ratio well is no longer practical as it might have been when gas was of little value. Various methods are disclosed in U.S. Pat. Nos. 1,845,181; 3,410,217; 3,941,510 and 3,991,825, none of which would be practical for use in deep wells or for lifting heavy oil. Expansion of the gas would cool the heavy oil to a nonflowable condition and thereby lock up the tubing.
Therefore, some objects of this invention are to provide methods, means, and systems to pump liquids from wells such that: vapor-lock of the pump does not occur; the pump is operated so as not to allow damage to pump parts caused by unnecessary contact with the produced fluid; the pump does not stroke unless the pump chamber is full of liquid; no sucker-rods are required to operate within a column of heavy-oil; no recirculation of a fluid to the pump is required; the pump chamber pressure may be reduced to as low as atmospheric pressure while formation fluid is flowing into the pump chamber so as to maximize the differential flowing pressure and thereby increase productivity of the producing formation; pumping of the well is effected with substantial savings of energy.
The first paragraph of U.S. Pat. No. 3,123,007 discloses a pump "employing a reciprocating column of liquid to operate the reciprocating plumger or traveling valve of a pump", in the first paragraph thereof, and as discussed in column 1, line 36, "The present invention provides an actuator for a well pump of conventional design". The same patent also discloses the actuator to employ an annular piston as in column 1, line 56. Many other patents disclose similar devices but lack the intelligence in the downhole pump itself to sence when the pump chamber is full of liquid, as does the subject invention.